Digital video transmissions over data communications and broadcasting networks demand high bit rates. The bit rate needed to transmit an individual video sequence with good quality depends on the image content and varies in time. As an example, sport programs typically need more data rate than cartoon when both are compressed with similar subjective quality. Scenes with high motion and full of detail require usually the highest data rates. Conventional encoding systems assign fixed data rates to each program, therefore content providers have to compromise between transmission capacity and image quality or waste data capacity. Especially in wireless transmission and broadcasting systems bit rate requirements are considered the major constraints of those systems and an economical dealing with resources is required. DVB-H (Digital Video Broadcast-Handheld) broadcasting systems can share the same radio frequency and lower layer protocol stack with DVB-T (Digital Video Broadcast-Terrestrial) broadcasting systems. Both DVB-H and DVB-T use MPEG-2 Transport Stream as the underlying transport and multiplexing protocol. Different DVB-H programs require different data rates at each moment in time. The more DVB-H programs share the same MPEG-2 Transport Stream (also known as the Multiplex), the less probable is that all programs need a very high data rate at the same time. This fact is exploited by the multi-program encoder system developed by the Fraunhofer Heinrich-Hertz-Institute (HHI). The multi-program encoder system dynamically distributes the available data rate of the MPEG-2 Transport Stream among the different programs in an optimum way. This “Statistical Multiplex” reduces the mean data rate for each program typically by about 40%.
Although, the Statistical Multiplex approach of the Fraunhofer Heinrich-Hertz-Institute (HHI) has been testified to be useful in the context of IP datacasting over DVB-H, the Statistical Multiplex as proposed by the Fraunhofer Heinrich-Hertz-Institute (HHI) is however subjected to major disadvantages. The interoperability of the multi-program encoder system required to obtain the dynamic distribution of the available overall data rate of the MPEG-2 Transport Stream among the different DVB-H programs requires a complex architecture and control implementation.